diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index ef2ae14fa..52de75803 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -20,7 +20,7 @@ parameters:
         processTimeout: 300.0
     checkMissingIterableValueType: false
     ignoreErrors:
-        - '~^Parameter \#1 \$im(age)? of function (imagedestroy|imageistruecolor|imagealphablending|imagesavealpha|imagecolortransparent|imagecolorsforindex|imagesavealpha|imagesx|imagesy|imagepng) expects (GdImage|resource), GdImage\|resource given\.$~'
+        - '~^Parameter \#1 \$im(age)? of function (imagedestroy|imageistruecolor|imagealphablending|imagesavealpha|imagecolortransparent|imagecolorsforindex|imagesavealpha|imagesx|imagesy|imagepng|imagecolorat) expects (GdImage|resource), GdImage\|resource given\.$~'
         - '~^Parameter \#2 \$src_im(age)? of function imagecopy expects (GdImage|resource), GdImage\|resource given\.$~'
         # Accept a bit anything for assert methods
         - '~^Parameter \#2 .* of static method PHPUnit\\Framework\\Assert\:\:assert\w+\(\) expects .*, .* given\.$~'
diff --git a/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php b/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php
index 3e2baff6d..cf616eb75 100644
--- a/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php
+++ b/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php
@@ -162,6 +162,9 @@ class MemoryDrawing extends BaseDrawing
         }
 
         $mimeType = self::identifyMimeType($imageString);
+        if (imageistruecolor($gdImage) || imagecolortransparent($gdImage) >= 0) {
+            imagesavealpha($gdImage, true);
+        }
         $renderingFunction = self::identifyRenderingFunction($mimeType);
 
         $drawing = new self();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php
index 616ba9367..a2eb006d5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php
@@ -20,7 +20,7 @@ class SortByTest extends TestCase
      * @dataProvider providerSortWithScalarArgumentErrorReturns
      *
      * @param mixed $sortIndex
-     * @param mixed$sortOrder
+     * @param mixed $sortOrder
      */
     public function testSortByWithArgumentErrorReturns($sortIndex, $sortOrder = 1): void
     {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php
index 1cd2a138c..3145cfd3e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php
@@ -20,7 +20,7 @@ class SortTest extends TestCase
      * @dataProvider providerSortWithScalarArgumentErrorReturns
      *
      * @param mixed $sortIndex
-     * @param mixed$sortOrder
+     * @param mixed $sortOrder
      */
     public function testSortWithScalarArgumentErrorReturns($sortIndex, $sortOrder = 1): void
     {
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php
new file mode 100644
index 000000000..bbc7fe230
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php
@@ -0,0 +1,91 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
+
+use GdImage;
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
+use PhpOffice\PhpSpreadsheet\Shared\File;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Worksheet\Drawing;
+use PhpOffice\PhpSpreadsheet\Worksheet\MemoryDrawing;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx as XlsxWriter;
+use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
+
+class MemoryDrawingTest extends AbstractFunctional
+{
+    private string $outfile = '';
+
+    protected function tearDown(): void
+    {
+        if ($this->outfile !== '') {
+            unlink($this->outfile);
+            $this->outfile = '';
+        }
+    }
+
+    /**
+     * Test save and load XLSX file with transparent png.
+     */
+    public function testIssue3624(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $contents = file_get_contents('tests/data/Writer/XLSX/issue.3624b.png');
+        $stamp = MemoryDrawing::fromString("$contents");
+        $stamp->setName('Stamp');
+        $stamp->setHeight(120);
+        $stamp->setCoordinates('A2');
+        $stamp->setWorksheet($sheet);
+        $this->outfile = File::temporaryFilename();
+        $writer = new XlsxWriter($spreadsheet);
+        $writer->save($this->outfile);
+        $spreadsheet->disconnectWorksheets();
+
+        $reader = new XlsxReader();
+        $reloadedSpreadsheet = $reader->load($this->outfile);
+        $rsheet = $reloadedSpreadsheet->getActiveSheet();
+        $drawings = $rsheet->getDrawingCollection();
+        self::assertCount(1, $drawings);
+        foreach ($drawings as $drawing) {
+            if ($drawing instanceof Drawing) {
+                $path = $drawing->getPath();
+                $contents = file_get_contents($path);
+                $gdImage = imagecreatefromstring("$contents");
+                if ($gdImage === false) {
+                    self::fail('unexpected failure in imagecreatefromstring');
+                } else {
+                    self::assertTrue(self::checkTransparent($gdImage));
+                }
+            } else {
+                self::fail('Unexpected drawing not in Drawing class');
+            }
+        }
+        $reloadedSpreadsheet->disconnectWorksheets();
+    }
+
+    /**
+     * Determine if image uses transparency.
+     *
+     * @see https://stackoverflow.com/questions/5495275/how-to-check-if-a-png-image-has-transparency-using-gd
+     *
+     * @param GdImage|resource $im
+     */
+    private static function checkTransparent($im): bool
+    {
+        $width = imagesx($im); // Get the width of the image
+        $height = imagesy($im); // Get the height of the image
+
+        // We run the image pixel by pixel and as soon as we find a transparent pixel we stop and return true.
+        for ($i = 0; $i < $width; ++$i) {
+            for ($j = 0; $j < $height; ++$j) {
+                $rgba = imagecolorat($im, $i, $j);
+                if (($rgba & 0x7F000000) >> 24) {
+                    return true;
+                }
+            }
+        }
+
+        // If we dont find any pixel the function will return false.
+        return false;
+    }
+}
diff --git a/tests/data/Writer/XLSX/issue.3624b.png b/tests/data/Writer/XLSX/issue.3624b.png
new file mode 100644
index 000000000..48665d02c
Binary files /dev/null and b/tests/data/Writer/XLSX/issue.3624b.png differ